An Active Control Strategy For The Flow Past The Cylinder

The issue of flow around a bluff body has been widely investigated to cognize andto control the features of wake structure, because of the significance for the study oftheory and application of engineering. The features of flow around bluff body includessuch fundamental subjects as the boundary layer, separation, the free shear layer, thewake and the dynamics of vortices, and the flow around circular cylinder is one of thetypical problems. The problem of flow around circular cylinder mainly focuses ondecreasing the drag on the cylinder and suppressing the oscillation of the wake. Anactive flow control strategy, which is implemented by two symmetrical attachedcylinders with fixed rotation, and the attached cylinders are located in right behind themain cylinder, is proposed to reduce the drag and control the vortex structure, and theeffect on heat transfer has been investigated.In the present study, to study the influent on flow characteristics of the activecontrol strategy employed for two-dimensional unsteady flow, uniform flow past thecircular cylinders is simulated in this work. Numerical simulations are performed at avarious range of absolute rotational speeds (α) and different directions of rotation atReynolds number of200. The controlling of attached cylinders is achieved by theUser-Defined-Function. And the technology of dynamic mesh is implemented.The numerical simulation result indicates when the upper small cylinder is spinningclockwise, and the bottom attached cylinder is spinning counterclockwise, the purposeof prospective can be achieved. While the rotate direction of two affiliated cylindricalis adverse, the vorticity is reinforced and the drag and lift coefficients are increased.For the former, the percentage of pressure and friction drag has been furtherinvestigated along with the increasing of rotation parameter (α). When α equals to2.0,vortex shedding of main cylinder wake fluid is suppressed completely. And the fluidforces starts to tail off along with α increase, with a large drop for α=2.0.Moreover, the effect on the heat transfer is totally different between the two kindsof rotation directions of attached cylinders. When the upper small cylinder is spinningcounterclockwise, and the bottom attached cylinder is spinning clockwise, the heattransfer enhances because of strengthening the perturbation. However, for the otherrotation directions of two attached cylinders, the heat transfer reduces. Summing up the above, the optimum considering the reducing drag and enhancingheat transfer is determined by the specific requirements in the practical engineeringapplication.